1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, more particularly to a laminated layer type electrophotographic photosensitive member comprising a charge generation layer containing a charge generating material and a charge transporting material which receives and transports the carriers generated in the charge generation layer.
2. Related Background Art
In the prior art, as the electrophotographic photosensitive member, an inorganic photosensitive member having a photosensitive layer composed mainly of selenium, cadmium sulfide, zinc oxide, etc. has been widely used. These are not necessarily satisfactory in thermal stability, humidity resistance, durability, etc., and particularly selenium, cadmium sulfide are limited in production and handling due to toxicity. On the other hand, an organic photosensitive member having a photosensitive layer composed mainly of an organic photoconductive compound is attracting attention in recent years for having a number of advantages which compensate for the above drawbacks of inorganic photosensitive members.
As such organic photosensitive member, an electrophotographic photosensitive member having a photosensitive layer composed mainly of a photoconductive polymer as represented by poly-N-vinylcarbazole and a charge transfer complex formed from said polymer and a Lewis acid such as 2,4,7-trinitro-9 fluorenone has been practically applied. However, this photosensitive member is not necessarily satisfactory in sensitivity and durability.
On the other hand, the function separation type electrophotographic photosensitive member having the charge generation function and the charge transport function burdened separately on different substances, respectively, has brought about remarkable improvements to sensitivity and durability which have been the drawbacks of the organic photosensitive members of the prior art. Such function separation type photosensitive member can be very wide in scope of materials for respective charge generation substances and charge transport substances to be selected, and has the advantage that an electrophotographic photosensitive member having any desired characteristics can be produced with relative case.
As the charge generation substance, various azo pigments, phthalocyanine pigments, polycyclic quinone pigments, cyanine dyes, squaric acid dyes, pyrilium salt type dyes, etc. have been known, and among them, for azo pigments, a large number of structures have been proposed for such advantages as strong light resistance, great charge generation ability, easiness in preparation of the material, etc. Also, the present Applicant has previously reported disazo pigments having the benzanthrone skeleton in the molecular structure in Japanese Patent Laid-open Application Nos. 59-31962, 61-1219048 and 62-127845. These disazo pigments all proved to have high sensitivity as well as high potential stability, and could be sufficiently useful. However, further higher sensitivity and durability have been demanded for copying machines in recent years which have been made higher in speed, and the disazo pigments as described above cannot be said to be satisfactory.
In addition, as the printer by use of electrophotographic system, etc. has been widely used for output of microcomputer, wordprocesser, etc., a longer wavelength light source such as LED, laser diode has been used, and a photosensitive member useful for these light sources has been required. Particularly, when a laser diode is used for the light source, since the oscillation wavelength region of the laser diode varies depending on the difference between individuals, the temperature used, the temperature elevation by oscillation. The photosensitive member used is demanded to have flat spectral sensitivity in the oscillation wavelength region of the laser diode.
Particularly, in a printer or color printer, where gradation is considered to be important, selection of laser diode and laser temperature controller are required for suppressing the change in oscillation wavelength when the spectral sensitivity is not flat, the cost of these printers will be disadvantageously increased. Also for this reason, flat spectral sensitivity has been required.
As flatness of spectral sensitivity, the sensitivity change at from 760 nm to 800 nm which is the center of the oscillation wavelength region of laser diode is required to be within 0 to 15%, particularly desirably within 0 to 10%.
As the wavelength elongation technique of the azo pigment so as to correspond to such laser diode oscillation wavelength retion, the present Applicant has previously reported use of a specific coupler residue in Japanese Patent Laid-open Application No. 62-147463. However, the disazo pigment having benzanthrone within the molecule as disclosed in Japanese Patent Laid-open Application No 62-147463 has the change in spectral sensitivity at 760 nm to 800 nm of 20% at minimum, which cannot be said to be satisfactory, leaving room for improvement.